The present invention relates to a technique effectively applied to a high frequency power amplifier circuit and a radio communication device such as a cellular phone incorporating the high frequency power amplifier circuit, and more particularly to a technique for improving an output power level and power efficiency in a high frequency power amplifier circuit capable of controlling the power voltages of amplification transistors making up the high frequency power amplifier circuit to control output power.
A high frequency power amplifier circuit (in general, configured in multiple stages) that uses semiconductor amplifying elements such as MOS FET (Field Effect Transistor) and GaAs-MESFET is built into an output part of a transmitting side of a radio communication device such as a cellular phone (mobile communication device).
In a high frequency power amplifier circuit of this kind, generally, a semiconductor chip including transistors for amplification, their bias circuits, a power voltage control circuit, and the like are mounted on an insulating substrate such as a ceramic substrate to the surface and inside of which printed wirings are made, along with other semiconductor chips and discrete parts such as capacitances. Since the parts are coupled by the printed wirings and bonding wires so as to perform their respective required functions, the high frequency power amplifier circuit operates as if it were one electronic part.
The abovementioned electronic part is called an RF power module. However, instead of configuring the high frequency power amplifier circuit with plural semiconductor chips and discrete parts, it may be configured with one semiconductor integrated circuit and some external parts. This specification refers to such a semiconductor integrated circuit and the abovementioned RF power module collectively as a high frequency power amplifier circuit.
Cellular phones control output power (transmission power) so as to match ambient environments according to power level specification information from base stations so that output power is increased when distant from the base stations, and output power is reduced when near the base stations. In this way, a system is configured to prevent interference with other cellular phones.
Conventionally, some RF power modules of transmission output stages in cellular phones of the GSM (Global System for Mobile Communication) system are provided with an APC (Automatic Power Controller) circuit (see Patent Publication 1, for example). The APC circuit controls output power required for calls by detecting a DC level of output by a coupler, comparing it with an output level specification signal (Vramp), and feeding the result back to a bias circuit for generating an input bias voltage (gate bias voltage) of an output power element. This system is called a closed loop system.
On the other hand, the present applicant previously applied for an invention (Japanese Unexamined Patent Publication No. 2002-018646) on a high frequency power amplifier circuit that outputs signals corresponding to demanded output power levels by fixing a gate bias voltage and controlling power voltages Vdd1 of amplifying stages FET Q1, Q2, and Q3, based on an output control voltage (output level specification signal Vramp). This system (called a power voltage control system), which is an open loop system, is poorer in control precision but has the advantage of reducing circuit size, in comparison with the closed loop system.
[Patent Publication 1]
Japanese Unexamined Patent Publication No. 2000-151310